Soil Profile

The composition of different horizons in soil, from the surface vertically to where the land meets the rocks beneath, is called Soil Profile. In this article, we shall deal with the following:

- Soil Profile

- Kinds of soil

- Soil Moisture and its kinds

- Use of the soil moisture

- how to measure soil moisture

- important questions

The uppermost layer is called soil. It is the first layer of Earth, which can be seen with our bare eyes. It is the most critical component of the growth of the plant. The soil consists of essential minerals.

Soil Profile - Definition 

The soil profile layers can be easily identified by the texture and color of the soil. The topmost layer of the Earth’s crust is the soil. It is the most critical layer which comprises various minerals that are organic along with rock particles. These layers of the Earth’s crust help to grow and support plants. 

When the soil is formed, it gets settled in different vertical layers. These layers explain soil profile. 

Soil Profile – Types

These lead us to the various kinds of soil. The soil is divided into the following:

- Topsoil

- Subsoil

- Parent Rock

Layers of Soil

The soil scientists (also known as pedologists) have identified an exciting way to determine the soil profile model through the capital letters O, A, B, C, and E. All the above layers have unique and different characteristics from each other. 

Sometimes it is noted that this layer gets eroded due to various factors present in the environment like excess rain or wind can erode the top layer removing all minerals from the soil. 

The soil profile diagram shows the three major surfaces of the soil consisting of A, B, and C, which are the surface horizon, the subsoil, and the substratum. Again soil profile consists of an organic mineral coat at the surface (O). This surface provides the soil with all the natural minerals. 


The O-Horizon soil has organic materials like dried leaves, small rocks, fallen trees, and other organic matter that can be decomposed. It has about 20 to 30 percent of organic matter in it. The colour of the soil is generally black brown and dark brown due to the existence of organic matter.


The A-Horizon Layer consists of organic material and is famously called a humus layer. It is the uppermost layer of the soil that consists of dark decomposed matter, known as humus. 


The letter E denotes the master horizon, which is subsurface to all the layers of soil. It is present only in the forested regions. The colour of the soil is light. 


B-Horizon is also known as subsoil because of its presence below the topsoil. It is the layer of soil that absorbs all the rainwater that flows through the topsoil. It accumulates the rain for further usage. It has humus, organic matter, and soluble minerals.


Another layer of soil that presents below the C-Horizon; this layer consists of less weathered rocks or parent rocks. It doesn’t contain any organic substance in it. It is also known as saprolite.


R-Horizon is the layer that has partially weathered rocks or unweathered rocks. It is also known to be the foundation or the base layer of the soil. You can find manganese, granite, limestone, and basalt in this layer.

Soil Moisture

The water tenacity in the soil is called the soil moisture. The relevance of this coil moisture helps the plant extract the necessary minerals from the soil to grow. The soil absorbs water through various factors and also forms in the formation of the soil. When the water precipitates, it gets accumulated on the surface. The soil particles distributed on the surface helps to determine the porous nature of the soil. It helps in the vertical flow of the water to the regions below the surface. It is also called infiltration.

Soil Moisture – Types 

The following are the various types of water present in the soil forming the Soil Moisture:

- Gravitational Water

The free flow of water into the water table because of gravitational force is known as gravitational water. It is available for the plants to use as the water drains quickly if the soil is not compact. It can be found in the macropores of the soil.

- Hygroscopic Water

Hygroscopic Water is soaked from the atmosphere to the soil and is held firmly. Plants cannot absorb waters in large quantities, but they can still survive. 

- Chemically Combined Water

It is also known as combined water. After the removal of hygroscopic water because of the heat of the soil (150-degree Celsius), the remaining water changes its form into hydrate oxides of Iron, Silicon, etc.

- Capillary Water

The water that is remaining on the soil after the free flow gets wholly drained out. The laws of capillary movement come into the picture and change its form into a film that surrounds the grains.

- Atmospheric Humidity

Air carries a certain amount of water that is turned into vapour. It is measured in the form of vapour pressure or humidity. The ratio of vapour mass into the total mass of air derives from atmospheric humidity.

Soil Moisture: It’s Importance

  • The Soil Moisture is useful as it contains essential nutrients which is necessary for the growth of plants. 

  • It also helps in determining the yield of the crop in a particular region. 

  • It aids in controlling soil temperature. 

  • It also aids in soil formation. 

  • The moisture of the soil also creates biological events of the microbes that are there in the soil. 

  • The most important is that the Soil Moisture helps the plants during the process of photosynthesis.

Soil Moisture: How to Measure it?

The Soil Moisture can be Measured by the Following:

- Tensiometers

The Tensiometers measure the soil moisture’s tension. The tubes are filled with water with a porous ceramic tip added at the bottom. It is then sealed from the top that helps in creating a vacuum gauge. It is then put deep into the soil so that plants can absorb it quickly. The device is used to determine the availability of water percentage in the soil.

- Electrical Resistance Blocks

These blocks contain two electrodes that are linked with lead wires. It is extended to the surface of the soil. The blocks of the porous material carry the electrodes. The purpose of the device is to measure the tension of the soil water.

- Time Domain Reflectometry (TDR)

If you want to determine the content of the soil moisture, TDR is the device that you must use. You can place the steel rods in the soil and pass electrical signals deep into the soil. If the signals return, you can measure the water content of the soil.

FAQ (Frequently Asked Questions)

1. What is soil?

Ans: Soil is a complex mixture of vitamins, minerals, organic matter, organisms, and air. 

2. What is the Soil Profile?

Ans: Soil Profile is a profile that consists of all the secrets of soil. It is described as the vertical segment of soil that is surfaced by the soil pit.

3. Explain the Formation of Soil.

Ans: Soil is formed on the basis of soil minerals. The soil is produced from rocks that are the parent material. The soil is formed through the methods of weathering and erosion. 

4. What are Different Components of Soil?

Ans: The various components of soil are as follows:

  • Inorganic Minerals

  • Organic Matter

  • Water

  • Air

Why is Soil Profile Outstanding?

Ans: By explaining the soil profile, the weathering of soil and organic matter decomposition causes the soil profile. For example, infertile soil consists of a light-colored subsurface soil from where all the nutrients are leached away

6. What are the Various Horizons of the Earth?

Ans: The two primary types of horizons:

  • Earth-Sky Horizons

  • Celestial Horizons